1. Field of the Invention
This invention relates in general to a method and apparatus for making low carbon high chromium alloyed steels and in particular to a new and useful method of treating a high chromium low carbon melt with gaseous decarbonization agents while it is maintained at an underpressure and to an apparatus for carrying out the method.
2. Description of the Prior Art
In a known method for making low carbon high chromium alloyed steels by means of an underpressure treatment, molten steel having the approximate desired chromium content and high carbon content is first desulfurized in an electric furnace ladle and then treated by means of a recycle degassing arrangement. During the degassing oxygen is blown upon the melt in the ladle for oxidation of the carbon. This method enables a reliable contacting of the oxygen with the melt. However, when oxygen is blown upon the melt the chromium-oxygen equilibrium is exceeded at least locally whereby a chromium slagging occurs. This disadvantage is avoided by blowing oxygen upon chromium and carbon rich melt in a furnace maintained at underpressures. By the displacement of the carbon-oxygen equilibrium because of the underpressure to lower concentrations of the reaction partners below the equilibrium of the chromium slagging the carbon serves as a protective element. This method is disadvantageous inasmuch as the slag must be removed before the treatment of the melt and this is an increased expenditure that makes the completion of the melt a relatively costly operation which must be carried out in a vacuum melting furnace or a vacuum induction furnace which becomes blocked up during the entire making of the melt from the melting to the tapping. In another arrangement an efficient electric arc furnace is employed only during the time of the melting period. Other methods have the disadvantage that they are costly, particularly on large scales. None of the known methods disclose any efficient way of introducing the oxygen during the blowing without great losses.